In cellular networks, mobile user devices (e.g., mobile telephones) typically perform an initial “cell selection” process to identify and select a cell having a base station that is capable of adequately serving the user device. Because user devices may move from area to area, however, the base stations of different cells may become better positioned to communicate with the user devices at different times. Thus, in order to retain a high quality of service, cellular networks typically provide a mechanism for switching which cell serves a user device. When a user device is in active communication with a base station of a serving cell, or “connected,” the process of switching cells is typically referred to as cell “handover.” Handover is typically initiated by the serving cell issuing a “handover command” to the user device and the target cell. When a user device is in an idle mode (e.g., in a mode in which only overhead data such as paging messages, broadcast parameters, etc., are received from a base station of a serving cell), however, the process is typically referred to as cell “reselection.” While cell handover is generally instructed by the network, cell reselection is generally determined by the user device. The cell reselection process is typically initiated by the user device “registering” with the target cell.
In some cellular networks, such as cellular networks arranged according to the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) Specification, cells are uniform in size, constituting a homogeneous wireless network. However, in future generation mobile communication networks, such as 3GPP Release 10 and beyond, and other types of mobile communication networks, cells may vary in size, constituting heterogeneous wireless networks. Heterogeneous wireless networks may have both macro cells and small cells. Small cells may be pico cells, femto cells, or micro cells. Small cells are typically found inside and/or at the edge of the range of macro cells. The small cells can provide benefits, for example, such as increasing throughput and assisting in network load balancing. For example, if there is a particular area within the range of a macro cell with a high user density, such as a baseball stadium, a small cell can additionally be used in that area.
In homogeneous wireless networks, cell sizes are not considered for handover or reselection decisions. User mobility state is considered, typically based on the number of handovers or cell reselections over a given period of time, and typically handovers are designed to become more aggressive (i.e., criteria for handovers are made more lenient) when a user device is in a high-mobility state. This is because in a homogeneous wireless network aggressive handovers will result in early handovers for better signal quality. Celt reselection is typically done based solely on frequency and signal strength.